These are high quality machined steel mandrels. These are much stiffer then standard tube pins. They fit all types of tubes that we carry. They are intended to be used with a feed through/clamp down vise or vise tool. We carry them in 3 diameters .0310″, .0410″, .0620″, and all are 6″ long. The 6″ length allow customization of the length; just cut to the length that you like, or cut in half and you will have two sets! We sell them in one package of these three sizes.